Seasonal fluctuations of age classes, with application to South Russia, 1896-1897

ABSTRACT Seasonal variations in age class sizes involve those of births and those of mortality across ages. They affect censuses and, consequently, rates involving numbers by age. As their analytical expression becomes inextricable, a simulation of aging cohorts by months of age shows that mortality oscillations for human populations are not sufficient to prevent age classes from oscillating approximately like associated births, contrary to what previous literature suggests. The amplification converges after damping, and the level reached depends on the amplification of mortality oscillations relative to births between 0 and 6 months of age. The damping rate depends mainly on the amplification of the mortality of 0–5 months compared to births. The application to 1896 South Russian data shows that age class sizes vary during the year like the births of the associated cohorts and that the numbers counted at the census vary strongly according to the month of the census.